linux-kernel - Re: [PATCH v3 2/3] media: dt-bindings: alvium: add document YAML binding

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Date:   Tue, 6 Jun 2023 21:17:52 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Conor Dooley <conor@...nel.org>
Cc:     Tommaso Merciai <tomm.merciai@...il.com>,
        jacopo.mondi@...asonboard.com, martin.hecht@...et.eu,
        michael.roeder@...et.eu, linuxfancy@...glegroups.com,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Hans Verkuil <hverkuil@...all.nl>,
        Marco Felsch <m.felsch@...gutronix.de>,
        Gerald Loacker <gerald.loacker@...fvision.net>,
        Mikhail Rudenko <mike.rudenko@...il.com>,
        Shawn Tu <shawnx.tu@...el.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Benjamin Mugnier <benjamin.mugnier@...s.st.com>,
        Krzysztof Hałasa <khalasa@...p.pl>,
        Nicholas Roth <nicholas@...hemail.net>,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/3] media: dt-bindings: alvium: add document YAML
 binding

On Tue, Jun 06, 2023 at 07:07:42PM +0100, Conor Dooley wrote:
> Hey Laurent, Tommaso,
> 
> On Tue, Jun 06, 2023 at 07:36:56PM +0300, Laurent Pinchart wrote:
> > On Tue, Jun 06, 2023 at 05:54:03PM +0200, Tommaso Merciai wrote:
> 
> > > +  alliedvision,lp2hs-delay-us:
> > > +    maxItems: 1
> > > +    description:
> > > +      Low power to high speed delay time in microseconds.
> > 
> > You can drop "in microseconds", that's implied by the suffix.
> > 
> > > +      The purpose of this property is force a DPhy reset for the period
> > > +      described by the microseconds on the property, before it starts
> > > +      streaming. To be clear, with that value bigger than 0 the Alvium
> > > +      forces a dphy-reset on all lanes for that period. That means all
> > > +      lanes go up into low power state. This may help a csi2 rx ip to
> > > +      reset if that IP can't deal with a continous clock.
> > 
> > I'd like to propose what I think is a clearer version:
> > 
> >     description: |
> >       Low power to high speed delay time.
> > 
> >       If the value is larger than 0, the camera forces a reset of all
> >       D-PHY lanes for the duration specified by this property. All lanes
> >       will transition to the low-power state and back to the high-speed
> >       state after the delay. Otherwise the lanes will transition to and
> >       remain in the high-speed state immediately after power on.
> > 
> >       This is meant to help CSI-2 receivers synchronizing their D-PHY
> >       RX.
> 
> Question about the property.
> Why not make it have a minimum value of 1 and drop the special-case
> behaviour for zero?

The property is optional, so it can indeed be omitted if no delay is
desired. I have no strong preference on whether or not to allow 0 as a
valid value.

-- 
Regards,

Laurent Pinchart